I love Ronan. It has really grown on me lately. I think that would be a great choice.
As an aside your blinkie has my Oscar in it :) It makes me all sentimental seeing those little babies.
Hi Kiersten! Yay for ttc! Okay, so you want something Irish that is connected with Montana. Something that is uncommon and goes with Connor, Taryn and Aili. My suggestion is Fergus. The geographic center of Montana is in Fergus County (11 miles W of Lewiston, to be exact). I also like both Ronan and Finley for a boy, but the only Darby I know is a girl, so I probably think feminine for that. I think Troy would make a really great mn with any of your boy options.
I bet the weather is really nice in Montana these days. Enjoy!